This post is about some reasonably advanced type-level features of The Glasgow Haskell Compiler and as such I assume some knowledge of Haskell. Despite this I've made an attempt to link to further resources on Haskell features as I introduce them. My hope is that even if everything here doesn't make perfect sense...

Before we begin: in order to understand a lot of the following you'll first need some familiarity with Haskell syntax and be somewhat comfortable with what a Functor is. OK, now firstly: why learn about lenses? Every time I've seen lenses in action it's looked like wizardry. I mean, just look at these examples of...

Assuming you're a javascript dev who's had to deal with anything aysncronous. Firstly, we're going to talk about promises, so: What do we talk about when we talk about Promises? It's very likely you've done something like this: doSomethingAsync(function (resultOfAsyncThing) { console.log(resultOfAsyncThing) })...